New Delhi: The passing of the oldest known human being in the world – Emma Morano – in April this year at 117 years and the demise of Jeanne Calment of France at a record-setting age of 122 in 1997 intrigued scientists to delve deeper into the science behind human life span.


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The concept of maximum life span came into existence wherein scientists decided to find out exactly how long humans can live.


Human longevity has long since been a subject garnering immense curiosity despite a major study concluding that humans may have reached their maximum life span, arguing that the maximum reported human age at death had apparently generally plateaued at about 115.


Five separate research teams, however, have made their strong disagreement known after they found that the maximum human life span could far exceed previous predictions.


Published in a series of papers in the journal Nature, the papers present the case that there is no compelling evidence that we are approaching an upper limit on our mortality – or at the very least, that such a limit may be considerably higher than 115 years.


“I was outraged that Nature, a journal I highly respect, would publish such a travesty,” said James Vaupel, a demographer at the Max Planck Odense Center on the Biodemography of Aging in Denmark. Vaupel co-founded the International Database on Longevity, one of the databases analyzed in the previous study, Live Science reported.


Vaupel argued that the prior work relied on an outdated version of the Gerontology Research Group's database “that lacked data for many of the years they studied. Furthermore, they analyzed maximum age at death in a year, rather than the more appropriate maximum life span attained in a year — in many years, the world’s world's oldest living person was older than the oldest person who died that year.”


The person behind the previous study – Jan Vijg, a molecular geneticist at the Albert Einstein College of Medicine in New York – on the other hand, is quite adamant and stands firm behind his findings. This has ultimately led the disagreement to turn into a heated debate between both the sides.


“The evidence points towards no looming limit. At present the balance of the evidence suggests that if there is a limit it is above 120, perhaps much above – and perhaps there is not a limit at all,” Vaupel said.


Vijg is equally strident, implying that his critics are, to some extent, simply upset at being confronted with their own mortality, the Guardian reported.


As per the Guardian, the latest papers argue that this conclusion is wrong and offer a host of more optimistic interpretations. Prof Siegfried Hekimi from McGill University in Montreal said: “You can show the data are compatible with many different trajectories and not at all an ongoing plateau.”


Under one such scenario, lifespans would be predicted to climb steadily upwards, such that the oldest person alive by the year 2,300 would be expected to be 150 years old. “The increase in average lifespan will not suddenly crash into a 115-year limit,” he said.


Vijg, however, defended his team's October study. "We agree with none of the arguments put forward — sometimes because they were based on a misunderstanding, sometimes because they were plain wrong, and sometimes because we disagreed with the arguments themselves," he told Live Science.


One complaint was that Vijg’s analysis partitioned the data into two time periods – before and after 1995 – on the back of a visual inspection that appeared to show a levelling off around this year. When the two underlying trends were calculated, the period after 1995 had a flat gradient, appearing to confirm the hypothesis.


“That’s something you shouldn’t do in statistics,” said Hekimi. “It’s circular.”


Another problem is that when any data series is segmented, there may appear to be temporary plateaus or even declines, despite an overall upward trend – as seen in long-jump records, for instance.


Vijg said he accepts “absolutely nothing” in the latest criticisms, dismissing them as statistical nitpicking by those who “hadn’t read his paper properly”.He compared the suggestion that there was no lifespan limit in sight to Zeno’s paradox, where an arrow is shot at a tree and first travels half the distance and, from the halfway point, half the distance again, in an apparently unending journey.


“They try to come up with intricate models to show that mortality is actually decreasing with very old age,” he said. “It’s worse than science fiction,” the Guardian said.